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We reconstructed carbonate system parameters through multivariate linear equations in the Bransfield Strait, northern Antarctic Peninsula. We used hydrographic data (potential temperature, salinity, dissolved oxygen) and measured total alkalinity (TA) and total inorganic carbon (CT) to develop the best-fitted equations to reconstruct TA and CT in those stations where they were not available. With reconstructed TA and CT, the software CO2Sys v2 was used to reconstruct the other carbonate system parameters (partial pressure of carbon dioxide -pCO2, pH, aragonite and calcite saturation state). In this version, available data are: - longitude - latitude - pressure (db) - neutral density (kg m-3) - potential temperature (°C) - salinity - dissolved oxygen (umol kg-1) - total alkalinity(umol kg-1) - total inorganic carbon(umol kg-1) - partial pressure of carbon dioxide(uatm) - pH - aragonite and calcite saturation state

An earthquake swarm affected the Bransfield Strait, Antarctica, a unique rift basin in transition from intra-arc rifting to ocean spreading. The swarm, counting ~85,000 volcano-tectonic earthquakes since August 2020, is located close to the Orca submarine volcano, previously considered inactive. Simultaneously, geodetic data reported up to ~11 cm northwestward displacement over King George Island. We use a broad variety of geophysical data and methods to reveal the complex migration of seismicity, accompanying the intrusion of 0.26–0.56 km3 of magma. Strike-slip earthquakes mark the intrusion at depth, while shallower normal faulting the ~20 km long lateral growth of a dike. Seismicity abruptly decreased after a Mw 6.0 earthquake, suggesting the magmatic dike lost pressure with the slipping of a large fault. A seafloor eruption is likely, but not confirmed by sea surface temperature anomalies. The unrest documents episodic magmatic intrusion in the Bransfield Strait, providing unique insights into active continental rifting.

The Western Basin (WB) of the Bransfield Strait has a complex water mass structure derived from a variety of sources, and is located next to the Antarctic region most affected by climate change. The WB is one of the three Bransfield Strait deep basins and the one most directly influenced by the waters from the Bellingshausen Sea and Drake Passage. The objective of this paper is to study the variability of the inflow of water masses to the WB and to detect the possible impact of regional climate change. We focus on the modified Circumpolar Deep Water (mCDW) that enters the WB through the northwestern passages. To achieve this goal, this study uses historical hydrographic data collected between 1960 and 2014. Warming (0.0161 ± 0.0079 °C yr−1) and lightening (−0.0023 ± 0.0010 kg m−3 yr−1) of the mCDW core (γn = 27.85–28.27 kg m−3) are observed in the WB between 1960 and 2013. The waters within the 27.85–28 kg m−3 γn range presented warming and salinization. Waters deeper than 500 m showed cooling and freshening between the 1960s and 1990s; however, warming and lightening are observed if 1981–2013 is considered. These trends appear to be associated with the positive SAM trend observed since the mid-20th century. Statistically significant negative correlations between θ S and γⁿ of the mCDW core with ENSO were found between 1980 and 2014. During La Niña phases, the mCDW core extended along the southern slope of the South Shetland Islands while during El Niño phases, it was present in patches or was totally absent. Since the 2000s, the mCDW core extends southward within the WB, possibly associated to positive SAM phases. Statistically significant negative correlations between θ and S of the WB deeper waters with ENSO and SAM were found. These waters were in general more saline and denser during negative ENSO and SAM phases. Positive SAM phases with La Niña events suggest the increase (decrease) of mCDW (Weddell Sea shelf waters) contribution to the deep WB during the 2000s. Thus, high interannual variability in the thermohaline properties within the WB seem to be linked to the effect of these modes of climate variability on the source water masses. Fil: Ruiz Barlett, Eduardo Mariano. Ministerio de Relaciones Exteriores, Comercio Interno y Culto. Dirección Nacional del Antártico. Instituto Antártico Argentino; Argentina Fil: Tosonotto, Gabriela V.. Ministerio de Relaciones Exteriores, Comercio Interno y Culto. Dirección Nacional del Antártico. Instituto Antártico Argentino; Argentina Fil: Piola, Alberto Ricardo. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Sierra, Marta E.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Ministerio de Relaciones Exteriores, Comercio Interno y Culto. Dirección Nacional del Antártico. Instituto Antártico Argentino; Argentina Fil: Mata, Mauricio M.. Universidade Federal Do Rio Grande; Brasil

A remarkable shift in the species composition and size distribution of the phytoplankton community have been observed in coastal waters along the Antarctic Peninsula over the last three decades. Smaller photoautotrophs such as cryptophytes are becoming more abundant and important for the regional ecosystems. In this study, flow cytometry was used to quantify the smallest phytoplankton in the central Bransfield Strait and explore their distribution across the strait in relation to physical and chemical properties of the two major water masses: the warmer and less saline Transitional Zonal Water with Bellingshausen Sea influence (TBW), and the cold and salty Transitional Zonal Water with Weddell Sea influence (TWW). Pico- and nano-phytoplankton clusters were distinguished and enumerated in the cytograms: photosynthetic picoeukaryotes, cryptophytes (about 9 µm in size), and smaller (3 µm) nanophytoplankton. It was shown that nanophytoplankton developed higher abundances and biomasses in the warmer and less saline TBW. This biotope was characterized by a more diverse community with a pronounced dominance of Cryptophyta in terms of biomass. The results support the hypothesis that increasing melt-water input can potentially support spatial and temporal extent of cryptophytes. The replacement of large diatoms with small cryptophytes leads to a significant shift in trophic processes in favor of the consumers such as salps, which able to graze on smaller prey.

Age, growth and feeding habits of early life stages ofChionodraco rastrospinosusDewitt & Hureau, the most abundant channichthyid in the larval fish assemblages of the Bransfield Strait, were studied by otolith microincrement counts and stomach content analyses. Individuals measuring 39–69 mm standard length were caught in the uppermost depth strata down to 300 m from Brabant to Joinville islands along the northern Antarctic Peninsula. The sample consisted of post-larvae and juveniles aged 105–211 days, with a mean growth rate of 0.25 mm day-1. Larval size at hatching was estimated to bec.17.2 mm. Hatching was spread over a relatively long period from August–November. Sagittal otoliths were characterized by a strong check located at 23–52 microincrements of distance from the core, tentatively associated with the onset of first exogenous feeding. The relatively long period during which larvae can rely on yolk reserves and the large size at hatching enable them to utilize a wide size range of prey, as well as cope with occasional food shortages. The stomach contents consisted exclusively of euphausiids (furcilia and adults) and larvae ofPleuragramma antarcticumBoulenger. Based on growth rate, the residence time in pelagic waters of juvenileC. rastrospinosuswas estimated to be about a year and a half.

Surface deformation parameters and its use in volcano monitoring have evolved from classical geodetic procedures up to those based on Global Navigation Satellite Systems (GNSS), in particular the most widely used and known Global Positioning System (GPS), profiting from the automated data processing, positioning precision and rates, as well as the large storage capacity and low power consumption of its equipments. These features have enabled the permanent GNSSGPS data acquisition to ensure the continuous monitoring of geodetic benchmarks for the evaluation of surface deformation in active tectonic or volcanic areas. In Deception Island (Antarctica), a normal vector analysis is being used to give surface deformation based on three permanently observed GNSSGPS benchmarks. Due to data availability, both in the past and for near real-time use, all benchmarks used are inside the monitored volcanic area, although the reference is away from thermal springs and/or fumaroles, unlike the other two. The time variation of slope distances to the reference benchmark and of the magnitude and inclination of the normal vector to the triangle defined by the reference benchmark and any other two, provides the spatial deformation in the volcanic area covered. The normal vector variation in magnitude gives information on compression or expansion, here called spatial dilatometer, while the changes in inclination gives information on relative uplift or subsidence, here called spatial inclinometer. In geodesy, the triangle is a basic geometric unit and the areal strain is commonly applied in tectonics and volcanism. The normal vector analysis conjugates both, benefiting from the method's precision, simplicity and possibility to model the surface using several triangles. The proposed method was applied to GNSSGPS data collected every austral summer between 20012002 and 20092010 in Deception Island. The results evidence that Deception Island acts as a strain marker in the Bransfield Basin volcano-tectonic setting. Spanish Ministry of Education and Science as part of the National Antarctic Program; Recognition and fast evaluation of volcanic activity on Deception Island (GEODESY) [ANT1999-1430-E/HESP]; Geodetic Studies on Deception Island: deformation models, geoid determination and Scientific Information System [REN2000-0551-C03-01/ANT]; Acquisition of scientific software for GPS data processing [REN2000-2690-E]; Geodetic Control of the volcanic activity of Deception Island [CGL2004-21547-E/ANT]; Update of the Spanish Cartography for Deception Island [CGL2004-20408-E/ANT]; Volcanotectonic activity on Deception Island: geodetic, geophysical investigations and Remote Sensing on Deception Island and its surroundings [CGLl2005-07589-c03-01/ANT]; Geodetic and Geothermal Researches, Time Serial Analysis and Volcanic Innovation in Antarctica (South Shetland Islands and Antarctic Peninsula (GEOTINANT) [CTM2009-07251/ANT] info:eu-repo/semantics/publishedVersion

13 pages, 10 figures, 5 tables, [EN] During January 1994, the photosynthetic response (P–E curves) of phytoplankton in the eastern part of the Bransfield Strait (Antarctica) was studied in relation to the mesoscale hydrographic structures in the area. The most important hydrographic features found in the study area were: (i) the Bransfield Strait front which separates surface Bellingshausen waters from surface Weddell Sea water in the northern part of the Strait; (ii) further to the North, the Weddell–Scotia Confluence north of Elephant Island; (iii) to the South, the ice-edge and the associated lenses of melting waters at the south-eastern part of the sampling area. These three structures were associated with zones of shallower mixing depth (1 mg Chl m−3). The photosynthetic response of the phytoplankton was also affected by the hydrographic structures. The phytoplankton of the well-mixed Weddell waters showed a lower light saturation parameter (Ek100 μmol m−2 s−1). There were no differences in the light saturation parameters of phytoplankton samples from the different water bodies found in the region as demonstrated by a t-test for paired comparisons (0.88>P>0.46). The average Ek was 87±26 μmol m−2 s−1 and not significantly different (t-test NS, P=0.83) from the mean irradiance in the upper mixed layer (Zuml) without the Zuml≥150 m stations. The slope of the PmB vs. α relationship was 59±5 μmol m−2 s−1 (r2=0.66, P1.5 g C m−2 d−1 between King George Island and Elephant Island, [FR] Pendant la campagne en Antarctique du navire BIO Hesperides, effectuée en janvier 1994, dans la partie est du détroit de Bransfield (Antarctique), la réponse photosynthétique du phytoplancton (courbes P–E) a été etudiée en relation avec les structures hydrographiques à mésoéchelle correspondantes. Pendant cette période, trois structures hydrographiques principales ont été déterminées: 1) Le front séparant les eaux de Bellingshausen de celles de la mer de Weddell entre 62°30′S–56°30′W et 62°S–53°W, en direction SE–NE; 2) La Confluence Weddell–Scotia au nord de la région; 3) La zone marginale de la glace, avec des nappes superficielles d'eaux de fonte, à la partie sud-est de la zone de travail. Ces structures étaient associées à des zones de mélange superficiel de faible épaisseur (1 mg Chl m−3). La réponse photosynthétique du phytoplancton était également affectée par les conditions hydrographiques. Dans les eaux de la Mer de Weddell profondément mélangées, le phytoplancton présentait un paramètre de saturation de lumière plus bas (Ek100 μmol m−2 s−1). Il n'y avait pas de différences significatives entre les valeurs des paramètres de saturation de lumière des échantillons de phytoplancton provenant de différentes masses d'eau, comme on l'a demontré par la comparaison t-test des paires d'échantillons (0.88>P>0.46). Le EK moyen était 87±26 μmol m−2 s−1 et il n'avait pas de différences significatives (t-test NS, P=0.83) avec l'irradiance moyenne de la couche de mélange supérieure (Zuml), sans les stations avec Zuml≥150 m. La pente de la relation PmB vs. α (r2=0.66, P1.5 g C m−2 j−1 entre les Îles du Roi George et l'Île de l'Éléphant

Fifty-four specimens of pycnogonids belonging to twenty-two species, eight genera and six families were collected with a rocky dredge during the cruise Gebrap-96 in the central basin of Bransfield Strait, from depths between 647 and 1592 m. The richest station in terms of abundance and biomass was DR6 (south of Livingston Island), which was also the shallowest one; at this relatively shallow depth food is more available than in deeper waters. The families Nymphonidae and Colossendeidae had the same number of specimens (21 specimens; 39% abundance each). The most abundant species were Nymphon villosum and N. proximum. Pallenopsis buphthalmus was collected for only the third time. The collections increased the geographical distribution of three species and the depth range of six species. The volcanic structures sampled were inactive during 1996, since none of the specimens showed signs of hydrothermal phenomena. This collection was typically representative of the west Antarctic benthic zone. En la expedición Gebrap-96 se capturaron 54 picnogónidos pertenecientes a 22 especies, 8 géneros y 6 familias. Se prospectaron fondos del Estrecho de Bransfield, entre 647 y 1592 m con una draga de roca. La estación con más riqueza biológica fue la DR6 (sur de Livingston), la menos profunda de entre las prospectadas; a dicha profundidad hay más disponibilidad alimentícia que en aguas inferiores. Las familias más abundantes (Colossendeidae y Nymphonidae) tienen el mismo número de individuos (21; 39% abundancia cada una). Las especies más abundantes fueron Nymphon proximum y N. villosum, siendo Pallenopsis buphthalmus tercera cita mundial. Tres especies aumentan su distribución geográfica y seis su batimetría. El análisis de la picnogonifauna permite afirmar que las formaciones volcánicas permanecían inactivas en el año del muestreo, siendo esta fauna la típica de la Antártida occidental.

13 pages, 2 figures, 3 tables, As part of the FRUELA experiment, 11 sediment cores were recovered from the Bellingshausen Sea, the western Bransfield and Gerlache Straits (Antarctic Peninsula) to determine the spatial distribution of organic carbon (OC), biogenic silica (BSi), and nitrogen (N) in the sediment under regions of known irregular primary production rates (PPRs). OC, BSi, and N contents ranged from 0.3% to 1.2%, from 5.7% to 20.4%, and from 0.03% to 0.17%, respectively. Apparent mean sediment accumulation rates (SARs) varied between 0.25 and 3.11 mm year-1 (220 and 1750 g m-2 year-1). Central Gerlache and western Bransfield Straits (the Orleans Canyon) had the highest biogenic constituents contents and sediment accumulation rates, whereas the northern coast off Snow Island (Bellingshausen Sea) showed the lowest values. Central Gerlache Strait, with the highest primary production rates in the study area, was the only region where the OC and BSi contents in the sediment corresponded to the photosynthetic activity in the euphotic zone above it. At the extremes of Gerlache Strait as in western Bransfield Strait, sediment focusing by currents enhanced by depressions in the sea floor contributed to develop regions with high biogenic constituent concentrations, whereas at the Bellingshausen Sea and western Gerlache Strait, winnowing by currents may drift away the biogenic material exported from the euphotic zone. Apparently, bottom relief and currents rather than solely depth determined the modern distribution and accumulation rates of biogenic particulate matter in the study area. Paleoceanographic interpretations of the sedimentary record from Antarctic marginal seas, such as Gerlache and Bransfield Straits, should consider that focusing due to lateral transport and sea floor morphology and the preferential degradation of OC relative to BSi may increase to an important degree the biogenic contents in the sediment, especially the opal. OC and BSi accumulation in Antarctic marginal seas could be as important as the broad continental shelves despite large spatial differences. © 2004 Elsevier B.V. All rights reserved, The Comisión Interministerial de Ciencia y Tecnologı́a of Spain supported this research under contracts ANT94-1010, MAR96-1781-CO2-01, and ANT96-1346-E. This work was also benefited by the CONACYT (México) with the fellowship 92766

13 pages, 6 figures, 3 tables, [EN] Metabolic rates (oxygen consumption and ammonia excretion) of zooplankton were determined during the austral summer (January 1994), in the eastern Bransfield Strait. The study area comprised four distinct hydrographic zones: the ice edge on the western Weddell Sea, the waters of Weddell Sea origin, the southern part of the Weddell–Scotia Confluence, and the waters of Bellingshausen origin. The objectives were to estimate the fraction of primary production accounted for by the metabolism of salps and crustacean zooplankton, as well as the contribution of their excretion to the nitrogen demand of phytoplankton. Biomass-specific respiration and excretion rates of zooplankton were measured simultaneously by incubation methods at in situ temperatures. Zooplankton biomass was measured as organic C on aliquots of samples taken between 0 and 200 m. Primary production was measured by incorporation, using photosynthesis–irradiance relationships. Primary production ranged from 179 to 1612 mg C m−2 day−1. Salps were the most abundant zooplankton group, located mainly in the northern part of the study area, where they excluded other zooplankters. Their biomass ranged from 115 to 2930 mg C m−2 (0–200 m). On average, their metabolic carbon requirements represented about 5% of primary production per day, and their excretion of ammonia contributed 10% of daily phytoplankton nitrogen demand. Crustacean zooplankton were of minor importance in the study area, except at the ice edge and areas of recently melted ice. Their biomass ranged from 14.5 to 494 mg C m−2 and they required on average 0.9% of daily primary production, while ammonia excretion accounted for around 0.4% of the phytoplankton nitrogen demand. During this cruise, salps were the most important zooplankton group from the point of view of the transfer of biogenic carbon and nitrogen recycling. However, the control exerted by zooplankton on primary producers was overall modest, and most of the phytoplankton carbon probably sedimented out of the water column, This study was financially supported by the grant ANT93-0997 from CICYT (Spanish Commission for Science and Technology). The contribution of A.C. was funded by a fellowship from the Ministry of Education and Science

Ramos, Ana ... et al.-- 17 pages, 8 figures, 2 tables, [EN] BENTART 95 survey was carried out from January 12 to February 7, in the south off Livingston, in Deception Island and in a transect at the same geographical longitude covering from Drake Passage to Antarctic Peninsula. [...], [ES] BENTART 95 ha sido la segunda campaña que ha llevado a cabo nuestro país en aguas antárticas con el objetivo de estudiar las comunidades bentónicas y las condiciones medioambientales en que estas se desenvuelven. [...]

Quinto Simposio Español de Estudios Antárticos celebrado en 1993 en Barcelona.-- 7 pages, 3 figures, 1 table, [EN] The spatial distribution, species composition and abundance of ichthyoplankton in Bransfield Strait and adjacent waters was studied during a cruise on Antarctic spring 1991/92 season. [...], [ES] La distribución espacial, la composición específica y abundancia del ictioplancton en el Estrecho de Bransfield se estudió en una campaña realizada durante la primavera austral de 1991/92. [...]